JOMory November Blog post


It might seem like an afterthought at times, but the furnace filter is an important component of your HVAC system. Are you treating it as such? Perhaps you don’t know what you don’t know. Admittedly, it can be confusing, as there are a variety of sizes and options available on the market. It makes sense as a homeowner that you might have a question or two about furnace filters.

Don’t worry, we’ve done our best to distill this information into easily digestible content. This guide will help you understand furnace filters, how they function, and how to choose the best one for your home and HVAC system.

Q: What is the function of a furnace filter?
A: The furnace filter works to pull particles out of the air circulating in your home. As air circles through the ducts back to your HVAC unit, it makes its way through the filter. Pollutants such as dust, pet dander, dirt, and mold spores are trapped by the filter. Cleaner air then passes through to be conditioned by the HVAC system and is circulated back to your home, so you can breathe easier — literally.

Q: What are the different types of furnace filters?
A: Furnace filters, in general, come in two types: disposable or washable. Disposable ones can be removed from the unit and replaced with a new one as needed. Washable furnace filters are perhaps a more sustainable option in that they’re reusable. They can be removed from the filter cabinet, cleaned, thoroughly dried, and reinserted in the filter cabinet. Disposable furnace filter options range from fiberglass to high efficiency particulate arrestance (HEPA) types.

Q: What does MERV mean?
A: MERV is the rating system used to indicate the efficiency of a furnace filter. It stands for Minimum Efficiency Reporting Value. MERV ratings range from 1 to 16. The higher the MERV rating, the more efficient the filter at capturing contaminants of various sizes.

You should know that filters rated MERV 8 through 12 offer superior air filtration for residential homes. While you might be inclined to purchase the highest MERV-rated filter possible, this is actually not prudent. That’s because using these filters could restrict airflow through your HVAC system. You could end up facing uncomfortable conditions, increased energy consumption, and system breakdowns. If you have questions about which furnace filter is right for your home and HVAC system, we’d be happy to help advise you.

Q: How long do filters last?
A: The short answer: It depends. The service life of furnace filters is based on many factors. The efficiency rating of the filter greatly affects its performance and longevity. That means filters with higher MERV ratings typically last longer than lower rated, low efficiency filters.

Your lifestyle and health also enter the equation when it comes to a filter’s service life. In homes with pets or smokers, airborne contaminants are more prevalent at higher concentrations. You can expect filters will need to be changed more frequently and will become clogged faster. If you or someone in your family suffers from asthma or allergy, changing the filter more frequently can help reduce environmental triggers in the home and ease symptoms.

Seasonality also affects the frequency which a filter needs changed. For instance, on days when the outdoor temperature is extreme, the heating and cooling system is running more frequently than in the spring or fall. Air is circulating through the system and contaminants are constantly being pulled out from the air supply via the filter, causing it to clog faster. Therefore, the filter will need to be changed more often during these periods to maintain the integrity of the indoor air quality.

Q: When do I need to change my furnace filter?

A: Keeping the information above in mind, you can reference the following guide to determine when your furnace filter needs to be changed. The filter manufacturer will also specify how frequently it should be changed.

  • 1″ Furnace Filter: 1 – 3 Months
  • 2″ Furnace Filter: 1 – 3 Months
  • 3″ Furnace Filter: 6 – 9 Months
  • 4″ Furnace Filter: 6 – 9 Months
  • 5″ Furnace Filter: 9 – 12 Months
  • 6″ Furnace Filter: 9 – 12 Months


However, individual mileage will vary. That’s why it’s helpful to do a visual check of the filter, when in doubt, to ensure it’s not past its life. Some obvious signs also indicate your filter should be changed. They are as follows:
The filter appears gray, with dirt and debris visible on the surface.
You notice more dust throughout your home.
The furnace or air conditioner is running longer than normal.

Q: How do I find my size?
A: Your HVAC system is designed to work with a specifically sized filter. It’s best practice to use filters of the appropriate dimensions in your system. Most filters have their dimensions printed on the frame, in length x width x height format. For instance, the most common size furnace filters are 10×20.

When purchasing a replacement, note these dimensions and find one that fits the bill. If the dimensions are not printed on the filter, locate the model number. This will allow you to look up the dimensions so you can find a compatible filter.

Q: Will a furnace run without a filter?
A: Theoretically, you could run your HVAC system without a filter. However, this comes with some risk and it’s not a good idea for a few reasons. Without this safeguard in place, particles could go through the ductwork and end up collecting and sticking to the duct paneling. Because air is recirculated, this means those same containments are pumped back out in the remainder of the house. Gross!

Q: Can a dirty furnace filter cause headaches?
A: Yes. In fact, a dirty furnace filter can create a host of problems—both to your health and infrastructure. Headaches are a common complaint in homes without proper filter maintenance. When dust is not adequately removed from your indoor air, you can expect to suffer from colds and respiratory infections. Those with asthma might have more flareups, too.

Q: Where is my furnace filter located?
A: Filters are usually located near the blower, inside of the furnace. Remove the door panel and locate the filter, near a return duct or the blower. It’s important to turn off the furnace first before doing this task.

Your comfort is our top priority here at JO Mory. If you need help with selecting the right furnace filter, don’t hesitate to reach out. Our knowledgeable technicians will guide you in this important decision so you can stay comfortable and healthy, year-round!